This invention relates to a dispenser with an air pump mechanism which dispenses fluid using compressed air stored previously in a container.
A dispenser with an air pump mechanism which stores compressed air in a container by sliding a piston in a cylinder is well-known. In the known dispenser, a nozzle is moved downwards, not for pump operation, but only for opening a valve. When the nozzle comes down, liquid in the container is pressurized by compressed air and is continuously dispensed through the valve. During a dispensing operation the piston must be locked to reduce the projection from the dispenser as much as possible at the position where it is fully pushed in. However, a large force is required for locking because it is necessary for the piston to be pushed in against compressed air remaining in the cylinder. To remove such a defect, an air hole is adopted in a conventional method. The air hole is closed during pump operation and opened after the pump stops in order to release compressed air remaining in the cylinder into the atmosphere. By this arrangement, the resisting force against the piston locking is removed. However, this construction having such an air hole has the disadvantage of complicated pump operation because not only must the air hole be closed during pump operation, but also closure of the air hole must be maintained by adding a large force against residual compressed air.
A dispenser with an the air pump mechanism with no air hole for residual compressed air has been published in U.S. Pat. No. 3,955,720 (issued on May 11, 1976 to D. C. Malone). According to the Malone patent, a movable stem is installed in the inside of the piston and the stem is moved with the piston during pump operation. The tip of the stem keeps watertight the pressure chamber formed between a couple of valves by being in contact with the tubular sleeve installed in the inside of the piston. Compressed air remaining in the pressure chamber is released into the atmosphere through a clearance between the stem and sleeve, releasing the seal between them by moving the stem outwards independently of the piston and parting it from the sleeve. As mentioned above, according to the Malone patent, the dispenser has no air hole and it is not necessary to close an air hole; thus, pump operation is not complicated. Compressed air remaining in the pressure chamber can be easily released into the atmosphere. Furthermore, compressed air in the container can be released into the atmosphere by moving the stem inwards in the container independently of the piston, parting it from the sleeve, contacting it with the pressure accumulating valve of the couple of valves, and opening the pressure accumulating valve. However, since watertightness of the pressure chamber is accomplished by contacting the stem movable independently of the piston with the tubular sleeve fixed to the piston, the stem must be formed and arranged in accurate dimensions against the sleeve. In other words, the stem needs high accuracy in manufacturing and assembly.